Method of drying nodular fiberboard



ENToRs JOSEPH w aovL CHARLES R. CULP United States Patent METHOD OF DRYING NODULAR FIBERBOARD Joseph W. Boylan and Charles R. Culp, Lancaster, Pa.,

assignors to Armstrong Cork Company, Lancaster, Pa.,

a corporation of Pennsylvania Filed Nov. 29, 1968, Ser. No. 779,668 Int. Cl. F26b 7/00 US. Cl. 34-13 3 Claims ABSTRACT OF THE DISCLOSURE Wet nodular fiberboard is passed through two drying cycles to remove the moisture from the board, then the board is passed through a cooling cycle to remove the heat developed during the drying cycles. Both drying and cooling are accomplished by passing air through the boards. During the drying cycle, the air is heated and automatic controls are used to provide the proper amount of heat to remove the proper quantity of moisture.

BACKGROUND OF THE INVENTION Field of the invention The invention is directed to a drying apparatus for Wet nodular fiberboard. More particularly, the invention is directed to an automatic process for the passing of the drying air through the wet nodular fiberboard.

Description of the prior art The present technique for drying wet nodular fiberboard is to place the boards in a heated atmosphere wherein the water will evaporate from the boards. Usually a gas furnace is provided to produce a very high temperature atmosphere and air is permitted to circulate around the boards to cause the boards to dry by evaporation.

The nodular structure of mineral fiberboards does not lend itself readily to a structure which will permit air to pass through the boards. Also, the thickness of the boards does not lend itself readily to a drying technique that would utilize the passage of air through the boards. Consequently, drying techniques using the air-passthrough procedure are usually restricted to paper or fabric drying. The high temperature atmosphere technique has normally been used to dry mineral wool boards. This high temperature atmosphere results in the evaporation of the moisture from the wet boards. However, this technique is difiicult to control in that if the temperature gets too high, the board will be heat marked or browned; and if the air temperature is too low, not enough moisture will be withdrawn from the board. Also, measuring the condition of the board at the end of the drying cycle will not permit rapid change of the conditions within the dryer to rapidly correct the condition therein; and, consequently, an over compensation could result in a swinging back and forth between the extremes of wet boards to heat scorched boards.

The object of the invention herein is to provide a structure which will rapidly dry the nodular wet boards by passing the Warm air through the boards and read the condition of the air after it comes through the board to reflect the moisture content of the board and therefore provide a rapid change of the heating condition for the air so that properly dried boards can be secured.

SUMMARY OF THE INVENTION The invention consists of the process of drying Wet nodular fiberboards by passing the boards through at least two drying cycles and one cooling cycle. As the board passes through these cycles, air is used as the drying and cooling medium. Atmospheric air is taken into the ice apparatus performing the cooling cycle and removes heat from the boards. Naturally, this air picks up the heat. Instead of discharging this heated air to the atmosphere, the heated air is fed down towards the intake of the first drying apparatus. Additional heat is added to this air and it is fed through the apparatus performing the first drying cycle. The heated air passes through the board and removes moisture therefrom. Sensing means on the exhaust side of the board measures the condition of the air which in turn reflects the moisture content of the board. This sensing means is used to control the heating means which supplies heat to the incoming air. The air which is exhausted from the apparatus of the first drying cycle has been cooled to a degree, but is still elevated above atmospheric temperature. Consequently, this is fed through a reheating element and into the apparatus of the second drying cycle. The second drying cycle operates in the same manner as the first drying cycle and performs the final drying of the board. The board then passes on to the cooling apparatus where the board is cooled for further processing.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a schematic layout of the drying and cooling cycles and air flow therein.

DESCRIPTION OF THE PREFERRED EMBODIMENT The wet nodular mineral fiberboards 2 are placed on a wire-type conveyer structure 4. The conveyer structure may be of any particular structure which will permit passage of air therethrough. Consequently, the boards are supported on a structure so that air may be forced through both the board and its conveying structure. Arranged in line is a drying apparatus 6, a drying apparatus 8 and a cooling apparatus 10.

The board is transported by the conveyer through the first drying apparatus 6 wherein a substantial amount of the moisture is removed from the board. The board then passes to the second drying apparatus 8 wherein the remaining portion of the moisture is extracted from the board to provide the board with its desired dryness. Since the drying operation causes the board to develop an increase in temperature, the board must be cooled before further processing may be carried out. Consequently, the board passes from the second drying apparatus to a cooling apparatus 10, wherein air is forced through the board to cool it to a workable temperature. It should be noted that the two separate drying apparatus 6 and 8 could be combined in a single structure as long as the control structure is provided for sequentially controlling separate drying stages.

The air flow pattern to the drying and cooling stages is designed to carry out the pass-through or through circulation drying and cooling of the boards with the maximum economy in the use of air. Air is drawn from point 12, wherein the air is at its normal atmospheric condition, and pulled by blower 14 through the cooling apparatus 10 to cool the boards therein. The air passing through the hot boards cools the boards by picking up heat. Consequently, the atmospheric air entering the cooling apparatus at 12 emerges therefrom at the exhaust side 13 in a warm condition. The blower 14 then moves the air down to point 15 wherein the warmed air is passed through a heating device 16 to raise the air temperature to an elevated state. The air then enters at point 17 into the first drying apparatus 6. The air passes out of the apparatus for the first drying cycle at point 18 having been pulled therethrough by a blower 19. The air has picked up some of the moisture from the board, but is not in a fully saturated state. In passing through the board, the air has lost some of its heat. The blower 19 then passes the air along to a reheating apparatus which again raises the air to an elevated temperature. At point 21, the air then enters the second drying apparatus and passes through the boards to emerge at 22 having been pulled through the second drying apparatus by a blower 23. This heated, moisture laden air is then exhausted to the atmosphere at point 24. The air passing through the second drying stage has removed sufficient moisture from the board to put it to its desired state of dryness.

As the air moves through the wet mat, heat is transferred to the fiber structure, water is evaporated and the water vapor is carried away by the cooled air. It follows then that the air temperature on the underside or exhaust side of the mat reflects the moisture content condition of the mat; that is, for a low temperature of 160 F. there remains considerable moisture in the mat, while for a high temperature of 250 F. there is essentially zero moisture remaining in the mat. This phenomenon then provides the basis from which a controlled scheme has been devised which insures that all mats will be properly dried. A properly dried mat will be one which is of good color, having no discoloration and is dry. An additional desirable feature of any control system is that it would be sensitive to drying load changes. For example, as the moisture content fluctuates in the mats, the dryer should be made to respond to these fluctuations thereby providing an economical system which fires just hard enough to ensure mat dryness and never overfiring when low moisture content mats are present. Furthermore, during times of line stoppages or other difficulties which would require the conveyer to be stopped, this control system should automatically throttle back the heat to prevent mat and equipment damage. Upon restarting the conveyer, the system should advance the heat as required by the mats back to a normal condition without providing any wet or discolored mats.

The control system herein is based upon the use of at least two thermocouples 26 and 27, being provided on the exhaust side of the mat in each of the drying cycles. The apparatus of the second drying cycle would have corresponding thermocouples 26' and 27'. The thermocouples are used to measure the temperature of the air on the exhaust side of the mat. By the use of two thermocouples located approximately one inch from the mat, an average reading will be taken across the mat. This average reading is fed by conventional means to a conventional controller which adjusts the fuel mixture flow of the apparatus heating the incoming air. In the drawing, the thermocouples 26 and 27 control heater 16 while the thermocouples 26 and 27' control the reheater 20.

Consequently, as the temperature changes on the exhaust side of the heating apparatus, the air heating structures are adjusted to either cut down or increase the amount of heat being provided to the incoming air.

What is claimed is:

1. A process for drying wet nodular fiberboard comprising the steps of: passing the board through at least two drying cycles and one cooling cycle with the use of air as the drying and cooling medium, taking the air discharged from the cooling cycle, heating this air and using the heated air in the dryer of the first drying cycle to secure partial drying of the fiberboard, sensing the moisture content of the board by measuring the condition of the air on the exhaust side of the dryer to control the amount of heat added to the air entering the dryer, taking the exhausted air from the first dryer and passing it through a reheating means into the dryer of the second drying cycle, using this heated air to complete the drying of the fiberboard, sensing the moisture content of the board by measuring the condition of the air on the exhaust side of the second dryer to control the amount of heat added to the air entering the second dryer, and discharging the air from the dryer of the second dryer cycle to the atmosphere, whereby a nodular fiberboard is dried and cooled by an economically circulated air drying and cooling supply.

2. The process of claim 1 further including the step of passing the air through the fiberboard during the drying and cooling cycles.

3. The process of claim 2 wherein there is placed at least two thermocouples on the exhaust side of each of the dryers for sensing the average temperature at this point as the means for the measuring of the condition of the air on the exhaust side of the dryers.

References Cited UNITED STATES PATENTS 1,707,929 4/1929 Bennett 34-226 XR 2,671,968 3/1954 Criner 342l6 XR 2,874,482 2/ 1959 Haltmeier 34-48 XR 3,013,785 12/1961 King 34-48 XR 3,402,479 9/1968 Hohm et a1. 34-13 XR FREDERICK L. MATTESON, JR., Primary Examiner R. A. DUA, Assistant Examiner US. Cl. X.R. 3448 

